Polymeric films are commonly used in a variety of commercial and consumer goods. In particular, polymeric films have been used in disposable consumer goods such as disposable absorbent articles including diapers, catamenial products, and adult incontinence devices. These films are readily processable and can be used to improve exudate containment of the absorbent article. Furthermore, elastomeric films, which are polymer films exhibiting elastic properties, are commonly used in absorbent articles. Elastomeric films allow the absorbent article to provide a snug fit that can accommodate a range of different sized wearers and to provide a gasketing-seal to the wearer's skin. Elastomeric films are often combined with other materials such as nonwoven materials to form stretch laminates that may be used in absorbent articles.
Most polymeric films are supplied such that they need to be resized, laminated, or otherwise processed prior to incorporation into a consumer good. Generally, polymeric films are supplied in a bulk form such as a bulk roll or other configuration where multiple layers of the film are in face-to-face contact. However, one drawback of polymeric films provided as such is that the film tends to block or adhere together. Blocking can be permanent such that the force to separate the film layers exceeds the tensile strength of the film. Permanent blocking is seen where the film tears before the individual film layers separate. In some cases, the blocking may be reversible. The blocked films may be separated with an elevated unwind tension. However, the unwound film may have imperfections that are remnants of the blocking Blocking may be further exacerbated by storage at elevated temperature or pressure. Both conditions are common for storage of films supplied in bulk rolls.
Bulk rolls are often formed by winding the film onto a spool at some take-up tension that is imparted to the film. The outer concentric film layers apply a pressure to the inner layers. The bulk roll may remain in this configuration for several days, weeks, or months while being stored and/or shipped. The severity of blocking is also a function of the film's composition. Blocking is seen more frequently in a relatively soft film of poly(vinyl chloride) as opposed to a relatively hard film of high density polyethylene.
A variety of strategies have been used to reduce or eliminate the blocking effect in films. One strategy to reduce blocking involves compounding anti-blocking agents directly into the film composition. Generally, anti-blocking agents may be added into the polymer and blended to achieve thorough mixing. Often the mixing will occur at an elevated temperature so that the polymer and anti-blocking agent are molten or able to flow. Common anti-blocking agents include natural and synthetic silica, talc and other minerals, and organic compounds. One drawback with the compounding of anti-blocking agents is the potential for diminished properties such as tensile strength. For elastomeric films, anti-blocking agents can negatively affect the force profile of the film.
Another strategy to reduce blocking involves applying an anti-blocking agent directly onto a cast polymer film. Anti-blocking agents such as silicas (natural and synthetic), talc, and other minerals are commonly applied to the surface of films in a solid powder or particulate form. However, powder application to a film being conveyed at commercial speeds can result in a dusting problem. The dust can create an industrial hygiene and safety hazard for personnel working in proximity to the process. The powder may also contaminate the process line and downstream components. From a performance perspective, particulate anti-blocking agents may have poor abrasion resistance. The powder is held to the surface of the polymer film by the degree of tack exhibited by the film. Since the films may exhibit more cohesive than adhesive character (i.e., the film adheres to itself but not to other, dissimilar materials), the powder may be adhered loosely to the film. The powder may be removed from the surface of the film by abrasion or oscillation experienced in the process line. As a result, the powder treated film may still exhibit blocking.
Another strategy to reduce blocking involves the formation of a skin-layer on the polymer film. The skin layer may act as a physical barrier preventing self-contact of the polymer prone to blocking. It is known, especially for elastomeric films, that a polymer film prone to blocking can be coextruded with a thin skin layer of a polymer that is more resistant to blocking. As an alternative to an extruded skin, a low basis weight material, such as a nonwoven, may be used. The material is generally laminated to the film by some bonding means such as by use of an adhesive. Both types of skin layers have drawbacks. Given the large surface area over which a bulk rolled film may block, the skin layer generally is continuous over at least one surface of the film. As a result, a significant amount of material (e.g., anti-blocking polymer or nonwoven material) is needed to prevent the blocking of the film. Skin application requires additional process steps and complexity. Ultimately, the additional material and processing results in increased manufacturing cost.
In response to the above identified problems, it would be desirable to develop a method for combining an anti-blocking agent and a polymer film prone to blocking that does not require a coextruded or laminated skin layer, compounding of an anti-blocking agent, or powder application of an anti-blocking agent. Further, it would be desirable for the anti-blocking agent not to adversely affect the performance of the polymer film. It would also be desirable for the method to be applicable to both elastomeric and non-elastomeric films.